don't dart forgs get there poison from ants in their natural habitat? or least that's what i've read
i think common house ants would taste bitter and most amphibs would avoid them. actually there was a post on the caudata.org site about a spotted salamander getting stressed due to an ant infestation in the tanks

there are alot better foods theat are available in bait/pet shops: earthworms, wax worms, crickets, mealworms. i also have a live colony of pillbugs/sowbugs in my tank. they're harmless, high in calcium, and good recyclers(they eat waste including their own that is high in copper)